In many drilling operations to recover hydrocarbons, a drill string made by assembling pieces or joints of drill tubulars or pipe with threaded connections and having a drill bit at the bottom is rotated to move the drill bit. The entire drill string may be rotated using a rotary table, or using an over-ground drilling motor mounted on top of the drill string, typically known as a “top-drive.” As drilling progresses, a flow of drilling fluid, e.g., mud, is used to carry the debris created by the drilling process out of the borehole. Mud is pumped down the drill string to pass through the drill bit, and returns to the surface via the annular space between the outer diameter of the drill string and the borehole (generally referred to as the annulus). The mud flow also serves to cool the drill bit, and to pressurize the borehole, thus substantially preventing inflow of fluids from formations penetrated by the drill string from entering into the borehole.
As the drill bit penetrates into the earth and the wellbore is lengthened, more joints of drill pipe are added to the drill string. This typically involves stopping the pumping while the tubulars are added. The process is reversed when the drill string is removed or tripped, e.g., to replace the drilling bit or to perform other wellbore operations, pumping must be halted to remove each tubular from the drill string. Interruption of pumping may mean that the circulation of the mud stops and has to be re-started when pumping resumes. This can be time consuming, can cause deleterious effects on the walls of the wellbore being drilled, and can lead to formation damage and problems in maintaining an open wellbore.
To overcome this problem, methods for continuous circulation of mud have been developed. Current continuous circulation systems and methods use manual and hydraulically actuated valves, which add to complexity, weight, and controls.
Thus, a need exists for an improved apparatus, system, and methods that provide continuous circulation while adding or removing tubulars from a drill string.